Likely a bug in trimesh.visual.gloss.specular_to_pbr

[FrozenBurning]

According to the GLTF 2.0 specification, the metallicRoughnessTexture is stored as "green channel contains roughness values and its blue channel contains metalness values"

(https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#metallic-roughness-material).

However, in the conversion of specular_to_pbr (shown as below), the current implementation puts the metallic value to the R channel, which seems to be a bug.

trimesh/trimesh/visual/gloss.py

Line 363 in 563690a

[metallic, 1.0 - glossiness, np.zeros_like(metallic)], axis=-1